Head + Tail

Instead of select­ing the graph­ics acc­cord­ing to a fixed value (e.g. at step 65 select
file 65), we use a method that works with any given num­ber of files:

List all pdf-files in the tmp directory
with ls $TMP/*.pdf, take the amount accord­ing to the cur­rent grid type with head -n $GRIDTYPE,
take the amount accord­ing to the cur­rent step with head -n $GRAFIKCOUNT, select the last one
with tail -1.

This way we get a file, wether there are 1 or 500 in the folder.
If the gen­er­a­tor script did not pro­duce enough files, for any rea­son,
there is no need to have an excep­tion.
This soft select­ing method will com­pen­sate the error through.
Errors will not cause stop­pin but the change the visual output.